Synthesis of pterocellin A

The first total synthesis of pterocellin A (1) was achieved in 10 linear steps from commercially available kojic acid (6) and 2-bromo-3-pyridinol (11) in a convergent sequence. The key constructive steps are a directed lithiation to couple two pyridines and an intramolecular nucleophilic aromatic substitution to form 1. [structure: see text]     

Synthesis of poinsettifolin A

A synthesis of poinsettifolin A (1), a prenylated flavonol isolated from Dorstenia poinsettifolia, is described. Two routes starting from quercetin were explored, and 1 could be prepared if a prenyl group first was incorporated at C-6 of the protected quercetin followed by a condensation with citral at C-8. The key synthetic steps are a Mitsunobu reaction, an europium (III)-catalysed Claisen rearrangement coupled with cross-metathesis, and a benzopyran-forming geranylation. The two geranylated 3,5,3′,4′-tetrahydroxyflavonols prepared, 1 and 3, were assayed for antileishmanial activity against Leishmania amazonensis and Leishmania braziliensis, and found to be active. Compound 3 showed cytotoxic activity against leukaemia and lung cancer cells while 1 lacked cytotoxicity.     

Synthesis of azacridone A

[reaction: see text] The first total synthesis of the only known naturally occurring azaacridone alkaloid (1) has been achieved in 10 steps from phloroglucinol. A variety of ortholithiation reactions are described, and a method for overcoming the originally unfavorable regiochemistry of one of them is provided.     

Synthesis of bistramide A

We have developed an efficient and highly stereocontrolled synthesis of bistramide A, a selective activator of protein kinase C isotype delta. Our synthetic strategy featured a novel bidirectional approach for spiroketal construction based on the ring-opening/cross-metathesis sequence employing a highly strained cyclopropenone acetal. The synthesis afforded the final target with the longest linear sequence of 15 steps and provided unambiguous structural determination of bistramide A, including assignment of the previously unknown C(37) stereochemistry.     

Synthesis of adenophostin A

The natural product and potent agonist of the d-myo-inositol 1,4,5-trisphosphate receptor, adenophostin A, was synthesised from adenosine and d-glucose using efficient methodology. The synthetic material was equipotent with naturally occurring adenophostin A in evoking Ca²⁺ release from the intracellular stores of permeabilised cells.     

A Synthesis of Thalidomide

A synthesis of racemic thalidomide ( 1 ) was described and the important formal [3+3] cycloaddition strategy was a keystep. The total yield of thalidomide ( 1 ) was 18% in five steps from known 3 .     

Synthesis and Oxidation of N‐Aminoglyconolactams: A Synthesis of Mannostatin A

The N‐amino‐ribono‐1,5‐lactam 4 was prepared in two high‐yielding steps from the known methanesulfonate 2 . Oxidation of 4 with t‐BuOCl in the presence of 2,6‐lutidine afforded the tetrazene 6 (63%). Oxidation with MnO₂ gave the deaminated lactam 7 (40%), which was also obtained, together with the lactone 8 , upon oxidation of 4 with PhSeO₂H. Oxidation with Mn(OAc)₃/Cu(OAc)₂ provided the lactam 7 as the major and the dimer 9 as the minor product. Oxidation of 4 with 3 equiv. of Pb(OAc)₄ in toluene at room temperature gave two cyclopentanes, viz. the acetoxy epoxide 10 and the diazo ketone 11 in a combined yield of 78%. Oxidation with Pb(OBz)₄ provided 11 and the crystalline benzoyloxy epoxide 12 . The crystal structure of 12 was established by X‐ray analysis. The N‐amino‐glyconolactams 41, 46 , and 51 were prepared similarly to 4 . Their oxidation with Pb(OAc)₄ provided the diazo ketones 56, 57 , and 58 as the only isolable products. Oxidation of the N‐amino‐mannono‐1,5‐lactam 55 with Pb(OAc)₄ in the presence of DMSO gave the sulfoximine 59 . Mannostatin A, a strong α‐mannosidase inhibitor, was synthesized from the acetoxy epoxide 10 (obtained in 48% from 4 ) in seven steps and in an overall yield of 45%.     

A Direct Asymmetric Synthesis of Juglomycin A

Juglomycin A has been synthesized in four steps from 5-methoxy-1-naphthol.     

A Simple Synthesis of Oxaphospholes

Abstract

Stable derivatives of oxaphospholes were obtained from the reaction between electron-deficient acetylenic compounds and phenacyl bromide or its derivatives in the presence of triphenylphosphine in acetonitrile as the solvent in excellent yields.

GRAPHICAL ABSTRACT     

A Convenient Synthesis of Triquinacene

We have recently reported the synthesis of a derivative of triquinacene (2,3-dihydrotriquinacen-2-one (14)⁴) from Thiele's acid (1). Although this new synthetic route is simple in concept, it suffers from a large number of chemical steps. We wish to communicate an important overall simplification of this synthetic scheme which makes readily available triquinacene (22) and several of its derivatives.     

A Total Synthesis of Isosolanone

Nitroaldol reaction of acetone with nitromethane in the presence of base to give a nitroalcohol 3, followed by acetylation, and subsequent reduction of the resultant acetate 4 with NaBH₄ gave 2-methyl-1-nitropropane 5. Michael reaction of 5 in base with acrylonitrile to give nitronitrile 6, and Nef conversion of the nitro group resulted in the corresponding ketonic nitrile 7. Wittig olefination of the ketonic nitrile with 3-methyl-2-butenyl triphenylphosphonium bromide 8 gave dienenitrile 9, which upon treatment with MeLi, followed by acidic work up, provided isosolanone 2.     

Total Synthesis of Machilin A

Machilin A 9, a natural diarylbutane-lignan, was isolated from the bark and root ofMachilus thunbergii Sieb. et Zucc., which was used in traditional Chinese madicine'.This kind of lignan has shown various bioactivities and attracted organic chemists a greatattention2' 3.i. KMnO., 70-80 "C, lh. 88%, n. SOCI,, 95 "C, iii. CH,COCH,COOEt/NaOEt, THF, reflux. tv.NH.CI. EtOH, reflux, (n, iii, tv overall yield 78%), v. l, / NaOEt, THF, 98%, yi. PTSA, Benzene.reflux, 84%, vii. LAH, …